Information Processing Apparatus, Authentication Method, and Storage Medium

1. An information processing apparatus to which a storage medium is connected, wherein the storage medium is configured to store title keys configured to encrypt a content, a first application key and a second application key configured to encrypt the title keys for each application of the content, a media key block, an authentication key, and a media unique key; the media key block comprises encrypted media keys encrypted by different device keys; the first application key and the second application key are encrypted by the media unique key; the media unique key is obtained from a media key and a media identifier; the information processing apparatus comprises: a calculation module configured to read the media key block from the storage medium and to obtain an authentication key from the encrypted media keys; an authentication module configured to read the authentication key from the storage medium and to compare the read authentication key with the obtained authentication key in order to perform a mutual authentication; an update module configured to read the media unique key and one of the first and second application keys which is valid from the storage medium when the mutual authentication is successful, to decrypt the read application key by the media unique key of the storage medium, to re-encrypt a result of decryption by a media unique key of a host, to supply a result of re-encryption to the storage medium, and to update the other of the first and second application keys which is invalid; and a supply module configured to supply a media key block stored in the apparatus to the storage medium, and the storage medium comprises an update module configured to compare the media key block supplied from the information processing apparatus with the media key block stored in the storage medium in order to determine which is newer and to rewrite an old media key block stored in the storage medium with a new media key block supplied from the information processing apparatus.

2. The apparatus of claim 1 , wherein the storage medium comprises update count information of the media key block; the first application key is read and supplied to the information processing apparatus at odd numbers of update; and the second application key is read and supplied to the information processing apparatus at even numbers of update.

3. The apparatus of claim 1 , wherein a media key is obtained by computing a one-way function by the media key block read from the storage medium and a device key stored in the information processing apparatus; and a media unique key is obtained by computing the one-way function by the media key and an identifier of the storage medium.

4. The apparatus of claim 1 , further comprising: the calculation module comprises: a module configured to obtain a media key by computing a one-way function by the media key block read from the storage medium and a device key stored in the information processing apparatus; a module configured to obtain a media key prime by computing the one-way function by the media key and a constant; and a module configured to obtain an authentication key by computing the one-way function by the media key prime and an identifier of the storage medium.

5. An authentication method for an information processing apparatus to which a storage medium is connected, wherein the storage medium is configured to store an encrypted content, title keys configured to encrypt a content, first key management information which is updated whenever necessary and which comprises encrypted media keys obtained by encrypting a media key which is a base of an authentication key used for mutual authentication with another apparatus by using different device keys, a first application key and a second application key which encrypt the title keys for each application of the content, and update count information of the first key management information, the information processing apparatus configured to store second key management information which is updated whenever necessary, the method comprising the steps of: (i) reading the first key management information from the storage medium, collating the first and second key management information, sending the second key management information to the storage medium, when the second key management information is newer than the first key management information, and updating the first key management information to the second key management information; (ii) obtaining the authentication key from the first key management information read from the storage medium, and making mutual authentication with the storage medium by using the authentication key; (iii) sending a media key prime request to the storage medium, and obtaining an expected value of a media key prime response from the media key, when the mutual authentication is successful; (iv) obtaining a candidate value of a media key prime from a media key in the storage medium receiving the media key prime request, and sending the candidate value to the information processing apparatus; and (v) collating an expected value of the obtained media key prime and a candidate value of the received media key prime, and updating the first and second application keys alternately according to the update count of the first key management information, when the expected value coincides with the candidate value.

6. The method of claim 5 , wherein the (v) collating comprises: reading the first application key, encrypting the first application key by a media unique key obtained by computing a one-way function by the media key and a media identifier, and overwriting the encrypted application key on the second application key at odd numbers of update; and reading the second application key, encrypting the second application key by the media unique key, and overwriting the encrypted application key on the first application key at even numbers of update.

7. The method of claim 5 , wherein the (ii) obtaining comprises obtaining the authentication key by computing a one-way function by a media key prime and the media identifier, the media key prime being obtained by computing the one-way function by the media key and a constant.

8. An authentication method for a storage medium and an information processing apparatus, wherein the storage medium is configured to store title keys configured to encrypt a content, a first application key and a second application key configured to encrypt the title keys for each application of the content, a media key block, an authentication key, and a media unique key; the media key block comprises encrypted media keys encrypted by different device keys; the first application key and the second application key are encrypted by the media unique key; the media unique key is obtained from a media key and a media identifier; the authentication method comprises: reading the media key block from the storage medium and obtaining an authentication key from the encrypted media keys, by the information processing apparatus; reading the authentication key from the storage medium and comparing the read authentication key with the obtained authentication key in order to perform a mutual authentication, by the information processing apparatus; reading the media unique key and one of the first and second application keys which is valid from the storage medium when the mutual authentication is successful, decrypting the read application key by the media unique key of the storage medium, re-encrypting a result of decryption by a media unique key of a host, supplying a result of re-encryption to the storage medium, and updating the other of the first and second application keys which is invalid, by the information processing apparatus; supplying a media key block stored in the apparatus to the storage medium, by the information processing apparatus; and comparing the media key block supplied from the information processing apparatus with the media key block stored in the storage medium in order to determine which is newer and rewriting an old media key block stored in the storage medium with a new media key block supplied from the information processing apparatus, by the storage medium.